Power couplers are known and used widely in the microwave and millimeter wave (hereinafter collectively referred to as "microwave") art to divide power in an input path into two or more output paths. When energy flows in the opposite direction through a power coupler, the coupler acts as a power combiner. Known power couplers include the Lange coupler, branch line coupler, in-line coupler, split-tee coupler and the Wilkinson coupler, amongst others, and the present invention is applicable to all of these and to all other types of couplers. U.S. Pat. No. 4,254,386 for a Three Way Equal-Phase Combiner/Divider Network Adapted for External Isolation Resistors is illustrative of several of these types of couplers.
It is often desirous in power coupling to split an input signal equally between two outputs. In such a division, termed symmetric division, the power at each of the two output ports is half that of the input and the ratio of output power, often termed the split ratio, R, is 1:1 or 1 where the other of the output ports has been standardized to 1. In some instances, it may be desirous to split an input signal unequally such that the R value at two output ports is greater than 1, termed asymmetric division. In the context of microstrip transmission lines (a transmission media amongst others in which the present invention may be practiced), a split ratio of up to 3 (a 3:1 ratio) can be achieved with a conventional asymmetrical Wilkinson coupler, but values greater than 3 are difficult to obtain due to a practical characteristic impedance limit of approximately 100 .OMEGA.. For R values greater than 10, electromagnetically coupled lines have been demonstrated as working well. A need exists, however, for couplers having split ratios between 3 and 10. A need also exists for couplers with split ratios above 10 that have advantages over the prior art with respect to material, manufacturing, durability, size, performance, etc.
The present invention overcomes the shortcomings of the prior art with a reentrant power coupler that accommodates a range of split ratios of approximately 2&lt;R&lt;10, where the upper limit may extend above 10. The use of a reentrant design in a power coupler having direct electrical connections is not presently known.
In an embodiment of the present invention, the reentrant power coupler includes k input terminals, a plurality of m output terminals, where m is greater than k, and a network of n signal paths between the k input terminals and the m output terminals, where n is greater than m, due to a recombination of signal paths.
The reentrant power coupler of the present invention may comprise a signal propagating input terminal having at least a first and a second signal propagation section connected thereto; a first signal propagating output terminal having at least a third and a fourth signal propagation section connected thereto; a first signal path from the input terminal to the first output terminal that includes the first section coupled to the third section such that at least a portion of a signal input to the first section is propagated to the third section; and a second signal path from the input terminal to the first output terminal that includes the second section coupled to the fourth section such that at least a portion of a signal input to the second section is propagated to the fourth section; wherein the second signal path includes a bifurcation that propagates a portion of a signal passing therethrough to the fourth section and a separate portion of the signal passing therethrough to a second signal propagation output terminal.
In another embodiment of the present invention, the reentrant power coupler may comprise an input signal propagating segment approximately an odd multiple of one quarter of a design wavelength in length and having a first characteristic impedance; an output signal propagating segment approximately an odd multiple of one quarter of a design wavelength in length and having a second characteristic impedance that is approximately equal to the first characteristic impedance, the output segment having a common physical boundary along one side with the input segment; and a tap segment formed integrally with the input and output segments at the physical boundary, the tap segment having an approximate length of an odd multiple of one quarter of a design wavelength and a third characteristic impedance that is higher than the first or second characteristic impedances.
The coupler of the present invention may be practiced in both a generally planar or non-planar form and tap segments extending thereform need not be located at a common boundary between an input segment and an output segment thereof.
The present invention may also be achieved in several different embodiments and among the different coupler types, such as those cited above and those described below and combinations thereof.
The input may be any of various size Wilkinson-type couplers or some other bifurcating transmission line/waveguide configuration, such as hybrid ring coupler or the like. The characteristic impedance of the reentrant coupler is selected to provide a desired split ratio. Couplers are disclosed with multiple power taps. Multiple reentrant coupler combinations are also disclosed.
In yet another embodiment of the present invention, a reentrant coupler is formed of a plurality of cascaded transformer segments to enhance bandwidth.
The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings.